1. Field of the Invention
The present invention relates generally to the fields of molecular biology and immunology. More specifically, the present invention relates to DNA encoding the natural killer lytic associated protein ("NKLAP") and uses thereof.
2. Description of Related Art
Natural killer (NK) cells are large granular lymphocytes which lyse tumor and virus-infected cells without prior sensitization. Natural killer cells play a role in natural resistance against both solid tumors and hematopoietic tumors. M. Introna & A. Montovani, "Natural Killer Cells in Human Solid Tumors," Cancer Metastasis Rev., 2:337 (1983). In addition, natural killer cells have antimicrobial activity, giving them a role in combating diseases caused by bacteria, fungi, yeast, and protozoal parasites.
Although resident natural killer cells have the ability to kill select target cells in normal individuals, they are not able to kill most primary tumors. Natural killer activity decreases as a function of age, which may contribute to the incidence of tumors with age. It has also been found that natural killer cells from cancer patients are often incapable of killing tumor cells. Thus, a better understanding of the molecular and cellular events involved with natural killer lytic activity would facilitate medical treatment of many diseases.
While the receptor(s) involved in the recognition of target cells by natural killer cells are as yet undefined, it is well established that natural killer activity can be augmented by several agents, including certain viruses, cytokines such as the interferons ("IFNs"), and interleukins (IL-2, IL-12). J. Kornbluth, et al., "RG: Changes in Gene Expression Associated with interferon-.beta. and IL-2-Induced Augmentation of Human Natural Killer Cell Function," J. Immunol., 141:3234-3240 (1988). In fact, IL-2 and the interferons increase natural killer lytic activity 20 to 30 fold. These cytokines activate natural killer cells to kill with greater efficiency and a broader specificity. IL-2 activated natural killer cells are responsible for the majority of the lymphokine activated killing ("LAK") activity observed in vivo. J. H. Phillips, et al., "Dissection of the Lymphokine-Activated Killer Phenomenon: Relative Contribution of Peripheral Blood Natural Killer Cells and T Lymphocytes to Cytolysis," J. Exp. Med., 164:814-825 (1986). The killing activity of isolated natural killer cells from cancer patients may even be restored by culture with IL-2. A. Belldegrun, et al., "Interleukin-2 Expanded Tumor-Infiltrating Lymphocytes in Human Renal Cell Cancer: Isolation, Characterization and Antitumor Activity," Cancer Res. 48:206 (1988). However, a number of toxic effects associated with administration of high doses of IL-2 have been observed in treated cancer patients. M. Rosenstein, et al., "Extravasation of Intravascular Fluid Mediated by the Systemic Administration of Recombinant Interleukin-2," J. Immunol., 137:1735-1742 (1986). The augmentation of natural killer lyric activity by IL-2 and interferon is independent of DNA synthesis, but requires de novo RNA and protein synthesis. J. R. Ortaldo, et al., "Effects of Metabolic Inhibitors on Spontaneous and Interferon-Boosted Human Natural Killer Cell Activity," J. Immunol., 125:1839-1844 (1980). However, the molecules and mechanism involved in this enhancement have been unknown. Some researchers have theorized that one responsible mechanism is up-regulation of the adhesion molecules CD2, CD11a, and CD54. M. J. Robertson, et al., "Human Natural Killer Cell Adhesion Molecules: Differential Expression after Activation and Participation in Cytolysis," J. Immunol., 145:3194-3201 (1990).
Although many recent studies have begun to focus on early membrane signal transduction events associated with the binding of IL-2 and interferon to natural killer cells, it is still unknown how these events translate into increased tumor cell recognition and lysis. Molecular and biochemical studies have previously been hampered by natural killer heterogeneity and its low concentration in the blood. One mechanism by which natural killer cells are thought to kill tumor cells is through cell to cell contact wherein a Ca.sup.++ -dependent release of perforin from cytoplasmic granules occurs. J. D. Young, "Killing of Target Cells by Lymphocyte: A Mechanistic View," Physiological Rev., 69:250 (1989); P. A. Henkart, "Mechanism of Lymphocyte-Mediated Cytotoxicity," Ann. Rev, Immunol., 3:31 (1985).
According to this granule exocytosis model, the stages of cytolysis are: (1) recognition and adhesion resulting in the formation of effector-target cell conjugates; (2) reorientation of the microtubule organizing center and Golgi apparatus within the effector cell; (3) movement of granules towards the site of conjugation; (4) fusion of the granules to the cell membrane with subsequent release of granule contents into the intracellular space; and (5) target cell death, resulting from the formation of membrane lesions by the Ca.sup.++ dependent polymerization of perforin within the target cell membrane. Other mediators associated with natural killer lysis include serine esterase, natural killer cytotoxic factor, tumor necrosis factor (TNF) and TNF-like compounds. These molecules function in target cell lysis through mechanisms different from that of perforin, in some cases, inducing programmed cell death (apoptosis) in the target cells. The regulation of these events is largely unknown.
Previous attempts to identify and control the molecular and cellular events controlling natural killer and cytotoxic T lymphocyte lytic activity have been primarily unsuccessful. Consequently, an identification of the genes and their protein products associated with natural killer function is desirable. The prior art is deficient in the lack of effective means of treating neoplastic and auto-immune diseases. The present invention fulfills this longstanding need and desire in the art.